Crankcase oil leak- LD 150 '57
Posted: Mon Oct 12, 2026 3:28 pmHi all,
I have been mystified for some time at a persistent leak of oil into the crankcase, evidently from the gearbox-side oil seal. I think I have now identified this to the machined faces of the dual-race bearing (Casa code: M207, Innocenti code: 11110326). I should stress that this leak presented itself only after I had replaced the gearbox-side bearing with a new unit, at the same time as fitting a new crankshaft.
I'm posting this to see if anyone else has experienced the problem and / or is aware of the following details.
The first evidence of a problem was a smoky exhaust and engine failure. I initially identified an oily spark plug. Strip-down of the engine then confirmed gear oil in the crankcase.
Comparison of the new and old bearings shows a visible disparity at the tapered / rounded edges of the outer shell. Measurement determines the overall length is exactly the same; 20.5mm. However, the new bearing (marked SKF), has a flat face at the ends of the outer shell with an OD of 45mm. On the previous bearings (marked RIVA), that flat measures at 44mm OD.
The OD of this bearing is 47mm. The ID of the machined 'stopping point' in the engine case (at the point of entry into the gearbox), is 44mm.
The consequence of this disparity appears to be that the leading edge of bearing is seating fractionally less deep into it's aperture, which in turn causes insufficient compression on the outer O-ring seal, thereby allowing oil to enter the crankcase, behind the flange plate of the main oil seal.
I read that RIV bearings initially merged with SKF bearings in 1965. SKF fully acquired control of RIV in 1979.
Before addressing this issue with suppliers, I'm keen to know if anyone else has had a similar experience, or even has RIV and SKF bearings they can test these measurements on?
Thanks RP
I have been mystified for some time at a persistent leak of oil into the crankcase, evidently from the gearbox-side oil seal. I think I have now identified this to the machined faces of the dual-race bearing (Casa code: M207, Innocenti code: 11110326). I should stress that this leak presented itself only after I had replaced the gearbox-side bearing with a new unit, at the same time as fitting a new crankshaft.
I'm posting this to see if anyone else has experienced the problem and / or is aware of the following details.
The first evidence of a problem was a smoky exhaust and engine failure. I initially identified an oily spark plug. Strip-down of the engine then confirmed gear oil in the crankcase.
Comparison of the new and old bearings shows a visible disparity at the tapered / rounded edges of the outer shell. Measurement determines the overall length is exactly the same; 20.5mm. However, the new bearing (marked SKF), has a flat face at the ends of the outer shell with an OD of 45mm. On the previous bearings (marked RIVA), that flat measures at 44mm OD.
The OD of this bearing is 47mm. The ID of the machined 'stopping point' in the engine case (at the point of entry into the gearbox), is 44mm.
The consequence of this disparity appears to be that the leading edge of bearing is seating fractionally less deep into it's aperture, which in turn causes insufficient compression on the outer O-ring seal, thereby allowing oil to enter the crankcase, behind the flange plate of the main oil seal.
I read that RIV bearings initially merged with SKF bearings in 1965. SKF fully acquired control of RIV in 1979.
Before addressing this issue with suppliers, I'm keen to know if anyone else has had a similar experience, or even has RIV and SKF bearings they can test these measurements on?
Thanks RP